Incandescent lighting wastes 95% of the input energy as heat. The market has an extreme market need for high efficiency lighting to decrease energy consumption, and reduce greenhouse gases released to the atmosphere. This has led to banning inefficient bulbs in major economies. CFL and LED alternatives suffer from poor quality of light, poor color temperature, poor color rendering, high manufacturing costs, poor life if operated in a fixture with a heat trap, poor efficiency at end of life, flicker, require a power supply since they cannot operate from line voltage, and pose hazardous and electronic waste environmental impacts.
InfraRed Recycling (IRR) coatings have been added to incandescent lights. IR wavelengths are reflected back to reheat the filament, while visible wavelengths pass. Practical limitations have prevented adoption of this approach.
In U.S. Pat. No. 6,087,775, the IRR is formed on a section of an ellipsoid bulb, surrounding an approximately cylindrical filament. However, view factor is poor. There is high light leakage around the filter. Filament centering is a concern. The complexity of the filter is limited, as only simple filters may be practicably formed on a curved bulb.
Alternatively, in U.S. Pat. No. 8,823,250, the IRR may be formed on a flat substrate for use with flat filaments. This allows the use of more complex filters. The view factor is reasonable, but only if the filters are placed so close to the filament as to limit orientation of operation of the lamp to vertical only to prevent a hot filament from sagging into the filter. It also suffers from leakage of light from the sides of the filters.